I am working on a home in the warm humid region of the IECC designated zone 3. The finished room over the garage has kneewalls that currently have R-13 kraft-faced fiberglass batt insulation in the stud cavities. I would like to add at least 1" to 2" of rigid foam board, preferably polyiso, in order to reduce air infiltration and increase the walls thermal resistance. I am concerned that I may initiate condensation issues within the wall cavities by combining the kraft-faced vapor retarder with the vapor barrier properties of the polyiso. The kraft paper retarder faces the conditioned space and is in contact with the back side of the 1/2" drywall air barrier. I intend on fastening the foam board directly over the studs on the unconditioned side of the kneewall and taping all of the seams. Will I instigate moisture and trap it in the stud cavities if this is done? Can I use...